This invention concerns improvements in and relating to methods and apparatus for investigating emissions, particularly, but not exclusively in relation to gamma emissions.
During a number of tasks involving radioactive materials it is desirable to be able to accurately determine the position and level of radioactive materials within an environment. The environment may be a room or vessel in which operations involving radioactive material have been conducted and/or situations where decommissioning is required. To enable efficient decommissioning and/or to ensure man access under appropriate conditions to such environments accurate level and positional information is needed.
It is known to use a collimated gamma detector of the type referred to in EP 0542561 or WO 98/52071 to investigate gamma contamination. To achieve information about the sources of radiation the detector is collimated to give a conical field of view, with apex angle of less than 10xc2x0. This necessitates a significant length for the collimator. Furthermore, as the counts arising from the field of view must be very much higher than those penetrating the collimator from other directions to ensure meaningful measurements, the collimator must present a substantial thickness of material, 50 mm or more, around the detector. As a consequence the collimator alone has a substantial mass, 40 kg. The physical dimensions and properties necessary to achieve successful operation thus impair or prohibit the use of such instruments in locations for which access is limited, by the size of available entrance apertures for instance. Specific new entries to such locations are thus needed in such prior art systems or limited information on the radioactive materials must be tolerated.
The present invention has amongst its aims to provide an instrument which is capable of introduction into environments for which access is awkward or impaired. The present invention has amongst its aims to provide accurate and detailed information. The present invention has amongst its aims to operate and be capable of achieving such results in a practical time period.
According to a first aspect of the invention we provide a method of investigating emissions from radioactive sources in an environment, the method comprising:
providing an instrument, the instrument having a detector assembly, the detector assembly including a detector, preferably a single detector, which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector, and a moveable shielding component which is moveable relative to the field of view;
introducing the detector assembly of the instrument into the environment;
obtaining a signal count and/or count rate from the detector with at least a part of the environment with the field of view, the moveable shield being out of the field of view, the result forming the reference count and/or reference count rate for that given field of view;
obtaining a signal count and/or count rate from the detector for the given field of view, with a part of the given field of view occluded by the moveable shielding component, the result forming the partially occluded view""s count and/or count rate for that given field of view with that given part occluded;
for a given occluded part of a given field of view, the reference count and partially occluded view count and/or reference count rate and partially occluded view count rate being considered against one another to provide information about the emissions arising from the given field of view.
The first aspect of the invention may include any of the features, options or possibilities set out elsewhere in this document including the second aspect of the invention.
The first aspect of the invention may particularly include obtaining a signal count and/or count rate from the detector with at least part of the environment within the field of view, the moveable shielding component being out of the field of view; moving at least part of the detector assembly to place at least another part of the environment within the field of view and obtaining a signal count and/or count rate from the detector for that field of view, the moveable shielding component being out of that field of view; considering the counts and/or count rates obtained from the two or more different fields of view and selecting one or more areas of the environment for further investigation; the reference count and/or reference count rate being obtained for at least part of a selected area of the environment.
According to a second aspect of the invention we provide a method of investigating emissions from radioactive sources in an environment, the method comprising:
providing an instrument, the instrument having a detector assembly, the detector assembly including a detector which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector, and a moveable shielding component which is moveable relative to the field of view;
introducing at least the detector assembly of the instrument into the environment;
obtaining a signal count and/or count rate from the detector with at least part of the environment within the field of view, the moveable shielding component being out of the field of view;
moving at least part of the detector assembly to place at least another part of the environment within the field of view and obtaining a signal count and/or count rate from the detector for that field of view, the moveable shielding component being out of that field of view;
considering the counts and/or count rates obtained for the two or more different fields of view and selecting one or more areas of the environment for further investigation;
obtaining a signal count and/or count rate from the detector with at least a part of a selected area of the environment within the field of view, the moveable shield being out of the given field of view, the result forming the reference count and/or reference count rate for that given field of view;
obtaining a signal count and/or count rate from the detector for the given field of view, with a part of the given field of view occluded by the moveable shielding component, the result forming the partially occluded view count and/or count rate for that given field of view with that given part occluded;
for a given field of view and a given part occluded, the reference count and partially occluded view count and/or reference count rate and partially occluded view count rate being considered against one another to provide information about the emissions arising from the given field of view.
The first and/or other aspects of the invention may include any of the features, options or possibilities set out elsewhere in this document, and in particular in the following statements.
Preferably the method of investigating emissions is a method for determining the position of one or more radioactive sources in an environment which generate emissions and/or a method for determining the level of emissions arising from one or more radioactive sources in an environment. The method may achieve one or both of these measurements for at least part of a field of view, preferably all, with the detector in a fixed position relative to the environment during the measurement. The method may achieve one or both of these measurements by using a single field of view for the instrument. The method may achieve one or both of these measurements by occluding a non-converging, preferably diverging part of the field of view. The method may achieve one or both of these measurements by occluding a single part of the field of view of the instrument for each partially occluded view count and/or count rate obtained.
The emissions may be alpha and/or beta and/or gamma emissions, but are preferably gamma emissions.
The radioactive sources may be nuclear fuel, components used in the manufacture thereof, spent nuclear fuel, components thereof, fission products, radioactive waste, residues or the like.
The environment may be a room, chamber, cell, vessel, container, pipe, conduit, nuclear reactor core or part thereof.
The detector assembly preferably provides support for the detector, shielding for the detector and moveable shielding component. Preferably the detector assembly provides means for varying the position of the detector and/or shielding for the detector and/or moveable shielding component. The position varying means may include a rotatable mounting for the detector and/or the shielding for the detector and/or the moveable shielding component. The rotatable mounting or mountings may allow rotation about two axis, preferably provided at 90xc2x0 to one another. The position varying means may include one or more drive means, for instance motors, for varying the position of the detector and/or shielding for the detector and/or moveable shielding component. A separate drive means may be provided for each direction of rotation, more preferably for each direction of rotation for each of the shielding for the detector and the moveable shielding component.
In one preferred embodiment of the detector assembly, particularly suited to the hereinafter mentioned first detector/detector shielding/moveable shielding component configuration, the detector and detector shielding are rotatably mounted about a first axis and the moveable shielding component is rotatably mounted about a second axis. It is preferred that these first and second axis are perpendicular to one another. It is preferred that a drive means, such as a motor, is provided for each of these axis. It is preferred that the first axis is substantially, for instance +/xe2x88x9210xc2x0, vertical. It is preferred that the second axis is substantially, for instance +/xe2x88x9210xc2x0, horizontal.
In a further preferred embodiment of the detector assembly, particularly suited to the hereinafter mentioned second detector/detector shielding, moveable shielding component configuration, the detector and detector shielding are rotatably mounted about a first axis and a second axis and the moveable shielding component is rotatably mounted about a first axis and a second axis. Preferably the two first axis are separate from one another and/or the two second axis are separate from one another. Preferably the two first axis and/or two second axis are parallel to one another. Preferably the two first axis are perpendicular to the two second axis.
The detector is preferably a gamma detector, for instance of the scintillator or semi-conductor type. Preferably the signals generated by the detector are conveyed to a location outside the environment for processing. It is preferred that a single detector is provided within the instrument. In this way, a single well defined field of view for the instrument is assured.
A detected emission may be an emission reaching the detector from the field of view and/or through the shielding. Preferably the contribution to the detected emissions from the field of view is at least five times, and more preferably at least ten times, the contribution of detected emissions passing through the shielding for the detector.
Preferably the greater level of shielding against emissions in one or more directions is provided by a collimator for the detector. The shielding may be of lead or tungsten. Preferably, other than in the field of view, the detector is provided with at least 15 mm and more preferably at least 20 mm of shielding between it and the environment. Preferably, other than in the field of view, the detector is provided with less than 40 mm and more preferably less than 32 mm of shielding between it and the environment. The detector may be provided with a consistent thickness of shielding between itself and the environment in all directions, other than those within the field of view. Preferably no shielding, excluding the moveable shielding component when present, between the detector and the environment is provided within the field of view.
In a preferred embodiment, particularly suited to the hereinafter mentioned first detector/detector shielding/moveable shielding component configuration, the shielding may include a first generally planar component and a second generally planar component with a gap between them, at least in part, defining the field of view. The surfaces of the planar components which oppose one another are preferably planar surfaces. The surfaces of the planar components which oppose one another are preferably parallel with one another. The planar components may diverge away from one another, in the direction away from the detector. The outside surfaces, the non-opposing surfaces, of the shielding may be non-planar, for instance of greater thickness in proximity with the detector than distal from it, in one or more directions. The shielding may be provided with a dome, protrusion or other form of increased thickness in proximity with the detector, for instance an increased thickness along an axis of rotation of the detector and/or an axis of rotation passing through the detector. The shielding may be generally scalloped shape. Preferably the gap between the first and second component is closed by shielding around part of the detector to, at least in part, define the field of view.
In a further preferred embodiment, particularly suited to the hereinafter mentioned second detector/detector shielding/moveable shielding component configuration, the shielding may comprise a first conical portion. The first conical portion is preferably truncated at the end distal to the detector. The truncation is preferably perpendicular to the axis of the conical portion. The shielding may include a second conical portion, preferably abutting and ideally abutting at a corresponding diameter to the first conical portion. Preferably the second conical portion tapers, ideally away from the detector and/or in the opposing direction to the taper of the first conical portion. The second conical portion is preferably truncated at the end distal to the detector. The truncation is preferably perpendicular to the axis of the conical portion. The detector is preferably provided on the axis of the conical portion or conical portions. The detector is preferably provided on the plane defined by the junction of the first and second conical portions.
The detector may be provided with a field of view consisting of less than 30% of the potential views leading from the centre of the detector to the environment and the level may be more preferably be less than 25% or even less than 15%. Preferably the level is greater than 2% and more preferably greater than 5% or even greater than 10% of the potential views.
The field of view may be provided with a symmetrical cross-section. The field of view may be symmetrical in all directions, for instance a cone, or may have only restricted symmetry, for instance a slice.
The field of view, particularly for a conical field of view, preferably has an angular extent of less than 90xc2x0, more preferably less than 60xc2x0, and ideally less than 45xc2x0. Preferably the field of view has an angular extent of at least 5xc2x0, more preferably at least 15xc2x0, and ideally at least 25xc2x0. An angular extent of between 30xc2x0 and 40xc2x0 is particularly preferred. The angular extent may apply to one direction, or all for conical fields of view.
The field of view, particularly for a slice type field of view, preferably has an angular extent in the first direction of between 1xc2x0 and 15xc2x0, more preferably between 2xc2x0 and 10xc2x0 and ideally between 3xc2x0 and 8xc2x0. The field of view in a second direction, ideally the second direction being perpendicular to the first direction, may be between 45xc2x0 and 360xc2x0 and more preferably between 160xc2x0 and 200xc2x0. Preferably the angular extent in the first direction is constant throughout the angular extent in the second direction. In this way, a slice may be defined.
Preferably the moveable shielding component is provided of the same shielding material as the other shielding. Preferably the moveable shielding component has a substantially uniform extent, between the detector and the environment, within the field of view. Preferably the moveable shielding component obscures between 0.5% and 15% of the field of view, and more preferably between 5% and 10%.
Preferably the means for providing an optical image of the environment, and particularly the field of view, is provided as a part of the moveable shielding component. Preferably the means for providing the optical image of the environment is mounted on the moveable shielding component, ideally on the outside relative to the detector. Preferably the centre of the field of view of the means for providing an optical image of the environment lies on a line projected from the detector through the centre of the moveable shielding component. The means for providing the optical image may be a video camera and/or a still camera. Preferably a still image is used in the results display.
Preferably the moveable shielding component can be positioned at one or more locations outside the field of view. Preferably the moveable shielding component can be positioned at a plurality of positions within the field of view, more preferably positions throughout the field of view are facilitated and ideally sufficient positions to entirely cover the field of view, in total, are facilitated.
The detector assembly may be introduced into the environment by insertion through an aperture. The aperture may be of circular cross-section. The aperture may extend through a shielded wall into the environment. The aperture may have a maximum diameter and/or width of less than 200 mm, less than 150 mm or even less than 100 mm. The maximum width may be the diameter of the aperture. The detector assembly may be mounted on one end of a body with a portion of the body being retained in the aperture leading to the environment during measurement. The body may be supported within the aperture by one or more elements depending from the body, for instance legs which engage one or more walls of the aperture. The dependent elements may be provided with a rolling contact between themselves and the aperture wall or walls.
The detector assembly may be mounted on a tripod or other form of support. The tripod or other form of support may be deployed within the environment. The tripod or other form of support may be introduced to the environment by a robotic arm or other form of remote controlled manipulator.
A signal count and/or count rate for a field of view, with the moveable shielding component out of the field of view, may be determined using a count period of less than 5 minutes, more preferably less than 1 minute and ideally less than 30 seconds. Preferably the part of the environment in the field of view is fixed during the determination of a signal count and/or count rate.
Preferably the moveable shielding component is out of the field of view by being positioned at a location where shielding is provided between the moveable shielding component and the detector. Preferably the moveably shielding component is pivoted to this position. Preferably the part of the detector assembly moved to place at least another part of the environment within the field of view includes the detector and the shielding for the detector. The moveable shielding component may also be moved. The movement may be a rotation of that part of the detector assembly about one or more axis.
In one embodiment of the invention, particularly suited for the hereinafter mentioned first detector/detector shielding/moveable shielding component configuration, the detector, detector shielding and moveable shielding component are moved by rotation about a single axis. Preferably rotation is about a substantially vertically aligned axis, ideally without any rotation about any other axis.
In another embodiment of the invention particularly suited to the hereinafter referred to second detector, detector shielding, moveable shielding component configuration, the detector, detector shielding and moveable shielding component are moveable in rotation about one or both of two axis. Preferably rotation is about a first axis, with the position about the second axis fixed, until all desired fields of view at that fixed position for the rotation about the second axis have been considered. This may then be followed by a variation in the position about the second axis followed by rotation about the first axis to all desired fields of view.
Different fields of view may be considered sequentially, moving from one field of view to an adjoining one. An adjoining field of view may be horizontally and/or vertically adjoining and/or tilt angles for the detector and/or detector shielding may be changed to vary the part of the environment in the field of view.
Signal counts and/or count rates for a plurality of different parts of the environment may be determined by providing those different parts within different fields of view. Preferably signal counts and/or count rates for all parts of the environment for which investigation is required are performed. Parts of the environment may be investigated using overlapping and/or abutting fields of view. The environment may be divided into ten, fifty or even a hundred or more different fields of view.
The consideration of the counts and/or count rates from two or more different fields of view may involve considering those fields of view which produce high counts and/or count rates, and/or those fields of view which produce low counts and/or count rates and/or those fields of view which have counts and/or count rates above or below a threshold level. Preferably those fields of view relating to higher counts and/or count rates are selected. A higher count and/or count rate may be taken as indicative of one or more sources being within that particular field of view. A lower count rate may be taken as indicative of an absence of source from within that particular field of view.
The selected one or more areas for further investigation may in each case individually, be an area larger than any given field of view, any area corresponding to a given field of view or an area forming part of a given field of view.
The selection may also include the selection of one or more fields of view to investigate each of those one or more areas. The selection may involve selecting one or more of the previously measured fields of view for use in the further investigation and/or one or more fields of view not corresponding to a previously measured field of view. The field of view relating to a selected area may be a field of view for which a count and/or count rate has been determined before the selection of the areas is made and/or may be a new field of view. Where the field of view is a preexisting one, the previously obtained count and/or count rate may be used to form the reference count and/or reference count rate for that selected field of view. Where the field of view is a new one, a count and/or count rate from the detector for that field of view is obtained with the moveable shielding component being out of the field of view, that signal count and/or count rate forming the reference count and/or reference count rate for that selected field of view.
Preferably partially occluded view signal counts and/or count rates are obtained for a given field of view with a plurality of different parts of that given field of view occluded. Preferably the partially occluded view count and/or count rates for this plurality of different occluded views are considered together with the reference count and/or reference count rate for the given field of view to provide information about the emissions arising from that given field of view.
The method may include obtaining a signal count and/or count rate with each part of the given field of view occluded or only selected parts of the given field of view occluded, for instance where the area selected is smaller than the field of view.
Different partially occluded views are preferably obtained by moving the moveable shielding component within the field of view of the detector, preferably with the field of view of the detector fixed. The moveable shielding component may be made between each count and/or count rate determination by an amount less than its extent in the direction of movement, an extent equal to its extent in the direction of movement or by an extent in the direction of movement greater than its extent. Preferably the moveable shielding component has a fixed position during count and/or count rate determination. A count and/or count rate determination of less than 2 hours is preferred, more preferably less than 10 minutes and ideally less than 30 seconds.
In one embodiment of the invention, particularly suited for the hereinafter mentioned first detector/detector shielding/moveable shielding component configuration, it is preferred that the moveable shielding component is moved by rotation about a single axis, most preferably a horizontally aligned axis, and ideally with no rotation about any other axis. It is particularly preferred that the moveable shielding component be moved so as to occlude the entire extent of the field of view in one direction, for instance the entire width of a slice like field of view. Preferably the moveable shielding component is moved from one end of the field of view to the other, ideally occluding all the field of view over time.
In another embodiment of the invention, particularly suited for the hereinafter second detector/detector shielding/moveable shielding component configuration, the moveable shielding component is preferably moved by rotation about one or both of two axis. Preferably rotation is about a first axis, with the position about the second axis fixed, until all desired occluded views for that field of view at that fixed position for the second axis have been considered. This may then be followed by a variation in the position of the moveable shielding component by rotation about the second axis, followed by rotation about the fixed axis to all desired partially occluded views for the field of view.
Different occluded views may be considered sequentially, moving from one occluded view to an adjoining one. An adjoining occluded view may be horizontally and/or vertically adjoined.
Pan and/or tilt angles for the moveable shielding component may be changed to vary the part of the field of view which is occluded.
The consideration may involve determining which location or locations within the selected areas of the environment are significant contributors to the count and/or count rate, and/or determining which location or locations within the selected areas of the environment are not significant contributors to the count and/or count rate. The consideration may involve determining those parts of the field of view which when occluded result in the most significant decrease in the count and/or count rate for the given field of view.
The level of emissions may be determined based on the variation in count and/or count rate occurring with a part of the field of view occluded or not. The level may be indicated as a quantitative value and/or a range of quantitative values.
Preferably count rates are determined in the various stages.
Preferably the location of the source is determined in three dimensions. The location may be expressed in terms of determined by the tilt and pan angles of the detector assembly and/or the position within the environment indicated by the field of view for that count and/or count rate results. The location may also be determined in terms of the distance from the detector to the location. A range finding device may be employed on the instrument to assist in this determination. A laser range finder may be used.
The method may include taking video camera or camera images of the environment. The visual images may indicate the field of view under investigation by the instrument. Recordal facilities for the visual images may be provided. The information on the positions and/or levels of the sources may be indicated on the visual images.
In one embodiment, the collimator may be panned and/or tilted to various angles to provide different fields of view of the environment. Preferably the method includes sequentially moving the field of view by varying the tilt or pan angle and maintaining the other of the tilt or pan angle constant. In such a case, once the full range of the one of tilt or pan angles have been investigated at a respective pan or tilt angle, then the pan or tilt angle can be changed and the process repeated for the full range of tilt or pan angles. Preferably, particularly in such cases, the moveable shielding element may be adapted to be provided at various tilt and/or pan angles. In this way all of the different potential parts of the field of view may be occluded through suitably varying tilt and/or pan angles. Preferably one of the tilt and/or pan angles is kept constant and the other is varied to obscure sequentially the different parts of the field of view at that given constant tilt and/or pan angle. Preferably this is followed by a change in that tilt or pan angle and then variation of the other of the tilt or pan angle so as to scan the moveable shielding element across the field of view.
According to a third aspect of the invention we provide an instrument, the instrument having a detector assembly and signal processing means, the detector assembly including a detector which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector and including a moveable shielding component which is moveable relative to the field of view. The detector assembly being provided with a single detector.
According to a fourth aspect of the invention we provide an instrument, the instrument having a detector assembly and signal processing means, the detector assembly including a detector which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector and including a moveable shielding component which is moveable relative to the field of view, the field of view consisting of less than 30% of the potential view directions leading from the centre of the detector to the environment.
The third and/or fourth aspects of the invention may include any of the features, options or possibilities set out in the first and/or second aspects of the invention and/or elsewhere in this document.
The first and/or second and/or third and/or fourth aspects of the invention may include any of the features, options or possibilities set out in the fifth and sixth aspects of the invention below, and in particular may include the first and/or second orientation scans provided thereby before and/or after the sequence of the first and/or second and/or third and/or fourth aspects of the invention; and/or the further processing by statistical analysis.
According to a fifth aspect of the invention we provide a method of investigating emissions from radioactive sources in an environment, the method comprising:
providing an instrument, the instrument having a detector assembly, the detector assembly including a single detector which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector;
introducing the detector assembly of the instrument into the environment;
obtaining a signal count and/or count rate from the detector with at least a part of the environment within the field of view, the result forming the reference count and/or reference count rate for that field of view;
changing the orientation of the detector assembly;
obtaining a signal count and/or count rate from the detector with a further part of the environment within the field of view, the result forming a reference count and/or reference count rate for that further field of view;
the further field of view including only a part of the field of view within it;
the reference count and/or reference count rate for the field of view and the further field of view being considered to provide information about the emissions arising from that part of the further field of view which included part of the field of view within it.
Preferably the orientation is changed between obtaining the signal count and/or count rate for the field of view and further field of view by moving an axis of rotation for the detector assembly. Preferably the axis is moved by rotating the axis, ideally by rotating the axis through 90 degrees.
Preferably a signal count and/or count rate for one or more other fields of view are obtained, preferably prior to moving the axis of rotation of the detector assembly. Preferably the other fields of view are brought into view by changing the orientation of the detector assembly by rotating the detector assembly about an axis.
Preferably a signal count and/or count rate for one or more still further fields of view are obtained, preferably after the further field of view is considered. Preferably the still further fields of view are brought into view by changing the orientation of the detector assembly by rotating the detector assembly about an axis.
According to a sixth aspect of the invention we provide a method of investigating emissions from radioactive sources in an environment, the method comprising:
providing an instrument, the instrument having a detector assembly, the detector assembly including a single detector which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector,
introducing the detector assembly of the instrument into the environment;
obtaining a signal count and/or count rate from the detector with at least a part of the environment within the field of view, the result forming the reference count and/or reference count rate for that field of view;
changing the orientation of the detector assembly by rotating the detector assembly about an axis with the axis in a first orientation, so as to view one or more other parts of the environment;
obtaining a signal count and/or count rate from the detector for each of the other fields of view when the other parts of the environment are within view, the results forming a reference count and/or reference count rate for each of the other fields of view;
changing the orientation of the axis about which the detector assembly is rotated;
obtaining a signal count and/or count rate from the detector with a further part of the environment within the field of view, the result forming a reference count and/or reference count rate for that further field of view;
changing the orientation of the detector assembly by rotating the detector assembly about the axis with the axis in the changed orientation so as to view one or more still further parts of the environment;
obtaining a signal count and/or count rate from the detector for each of the still further parts when the still further part of the environment is within the field of view, the results forming a reference count and/or reference count rate for each of the still further fields of view;
one or more of the further field of view and still further fields of view including a part of the field of view and/or one of the other fields of view;
the reference count and/or reference count rate for the field of view, the other fields of view, the further field of view and the still further fields of view being considered to provide information about the emissions arising from those parts of the further field of view and/or still further fields of view which include at least a part of the field of view and/or other fields of view within them.
The fifth and/or sixth aspects of the invention may include any of the features, options or possibilities set out elsewhere in this document, but the following statements have particular relevance.
In one preferred embodiment the detector assembly is rotatably mounted about a first axis having a first orientation and a second orientation, the axis being moveable between the first and second orientations. The first and second orientations may be perpendicular to one another. It is preferred that a drive means, such as a motor, is provided to move the detector assembly between the two orientations. It is preferred that the first orientation provides a substantially, for instance +/xe2x88x9210xc2x0, vertical axis. It is preferred that the second orientation provides a substantially, for instance +/xe2x88x9210xc2x0, horizontal axis. The first orientation and/or second orientation may provide non-vertical and/or non-horizontal axes. The first orientation may provide an axis which is substantially, for instance plus or minus 10xc2x0, perpendicular to and/or substantially, for instance plus minus 10xc2x0 parallel to an edge and/or axis of the environment and/or an edge and/or an axis of a part of the environment. The part of the environment may be a conduit, passage, pipe, glove box, container, work surface, cable array. The second orientation may provide an axis which is substantially, for instance plus or minus 10xc2x0, perpendicular to and/or substantially, for instance plus or minus 10xc2x0 parallel to an edge and/or axis of the environment and/or an edge and/or an axis of a part of the environment. The first and/or second orientation may use axes which are perpendicular to one another, but non-perpendicular axes may be employed.
The method may include the selection of a first orientation and/or a second orientation. The selection may be based on the configuration of the environment and/or a part thereof, and in particular be based upon a junction, edge or axis alignment of the environment or a part thereof. Third, fourth or further orientations may be selected for scanning based on such features of the environment and/or a part thereof.
The detector and/or detector assembly may be moved relative to the environment between the first and second orientation. In particular the detector and/or detector assembly may be moved closer to a part of the environment. The detector and/or detector assembly may be moved by inserting the detector assembly into the environment to a further extent.
The position of the detector and/or a detector assembly relative to the environment in a first orientation and/or in the second orientation, the position being different between the two, may be used to provide further information about the emissions arising using a triangulation.
In a preferred embodiment, the shielding of the detector assembly may include a first generally planar component and a second generally planer component with a gap between them, at least in part, defining the field of view. The surfaces of the planar components which oppose one another are preferably planar surfaces. The surfaces of the planar components which oppose one another are preferably parallel with one another. The planar components may diverge away from one another, in the direction away from the detector. The outside surfaces, the non-opposing surfaces, of the shielding may be non-planar, for instance of greater thickness in proximity with the detector than distal from it, in one or more directions. The shielding may be provided with a dome, protrusion or other form of increased thickness in proximity with the detector, for instance an increased thickness along an axis of rotation of the detector and/or an axis of rotation passing through the detector. The shielding may be generally scalloped shape. Preferably the gap between the first and second component is closed by shielding around part of the detector to, at least in part, define the field of view.
The field of view is preferably consistent between the field of view, other field of view, further field of view and still further field of view, only the portion of the environment being viewed changing between them. It is preferred that the field of view be slice shaped, for instance defined by two non-parallel planes which oppose one another and two further non-parallel planes which oppose one another, the planes being separated by an arc in each case.
Preferably the field of view has an angular extent in the first direction of 10xc2x0 or less, more preferably 6xc2x0 or less and ideally between 4xc2x0 and 6xc2x0. The field of view in a second direction, ideally the second direction being perpendicular to the first direction, may be between 45xc2x0 and 360xc2x0 and more preferably between 160xc2x0 and 200xc2x0. Preferably the angular extent in the first direction is constant throughout the angular extent in the second direction. In this way, a slice may be defined.
The consideration of the counts and/or count rates from field of view and/or other fields of view and/or further field of view and/or still further fields of view may involve considering those views which produce high counts and/or count rates, and/or those views which produce low counts and/or count rates and/or those views which have counts and/or count rates above or below a threshold level. In particular the consideration may involve matching the field of view and/or the other fields of view with the further field of view and/or still further fields of view which produce high counts and/or count rates, and/or those views which produce low counts and/or count rates and/or those views which have counts and/or count rates above or below a threshold level. A match may suggest that the part of the further field of view and/or part of the still further fields of view within the field of view and/or other fields of view contains a significant source of radiation where a higher count or count rate is encountered or suggest a that the part does not contain a source of radiation where a lower count and/or count rate is encountered. A higher count and/or count rate may be taken as indicative of one or more sources being within a view. A lower count rate may be taken as indicative of an absence of sources from within a view.
The part of the field of view and/or other fields of view included within the further field of view and/or still further fields of view may be conical in shape, and in particular a square based cone, the detector being at the apex of that cone. The part may have an apex angle corresponding to the width angle of the field of view defined by the shielding.
Preferably the consideration suggests a location for the radiation within that part. The location of the source may be determined in three dimensions. The location may be expressed in terms of determined by the pan angles of the detector assembly in the first and second orientations and/or the position within the environment indicated by overlap between the field of view and/or other fields of view and the further field of view and/or still further fields of view. The location may also be determined in terms of the distance from the detector to the location. A range finding device may be employed on the instrument to assist in this determination. A laser range finder may be used. The information may provide an indication of one or more potential positions or locations of sources within the environment. The position and/or location may be expressed as an angle in one direction relative to a reference position and/or by an angle relative to a second reference position. In particular a horizontal angle and vertical angle may be used to indicate the location or positions where a single source is present preferably a single position and/or location is indicated. Where multiple sources are present, the information may include a set of locations and/or positions of which only some actually correspond to a source. The positions and/or locations in such a case may be expressed as an angle in a first direction and as an angle in a second direction, one or more of the angles in the first direction and/or in the second direction featuring as part of the location or position definition of two or more sources.
The information may be subjected to further processing, in particular to statistical analysis. The statistical analysis may involve comparison of the measured count or count rate for one or more of the fields of view against a predicted count or count rate for the field of view given a model source position and/or level and/or number of sources. The comparison preferably involves a plurality of the fields of view and ideally all of the fields of view from the first and/or second orientation. A least squares analysis may be used. Preferably alterations to the model source level and/or position and/or number of sources are made so as to minimise the difference between the measured count and/or count rates and the predicted count and/or count rates.
The measured count and/or count rates may be corrected according to one or more factors before the comparison is made. The correction factors may be based upon the response of the instrument, for instance of the detector, to one or more known source levels and/or positions and/or numbers. The correction factors may be based on the response of the collimator to one or more known source levels and/or positions and/or numbers.
Preferably the suggested location for the one or more sources of radiation within the environment is corrected based upon the model positions and levels which give counts and/or count rates which best correspond to the measured count and/or count rates.
Preferably two or more overlapping fields of view in the first and/or second orientation are used when statistical analysis is deployed. Preferably all of the environments scanned in the first and/or second orientation is included within at least two fields of view which contribute to the scan for that orientation.
The method may include taking video camera or camera images of the environment. The visual images may indicate the field of view under investigation by the instrument. Recordal facilities for the visual images may be provided. The information on the positions and/or levels of the sources may be indicated on the visual images.